The invention appertains to an air quantity metering apparatus and more particularly, to a fuel injection system of a combustion engine having a barrier flap which is pivotably mounted in a flow path on a shaft extending transversely of the flow path. A first restoring spiral spring element is wound around a free end of the shaft and has one end attached to a cam affixed to the shaft while the other end of the spring element is secured to the inner wall of a rotatable housing member, the outer periphery of which is formed with a plurality of teeth. An additional spring member is arranged to cooperate with the teeth on the rotatable housing member and functions together with the first restoring spring element to provide for pre-tensioning of the barrier flap and flow control in said flow path.
In commonly known air-quantity metering devices of this type, the securing of the spring housing, which is made of a synthetic material, is accomplished by squeezing it against the air metering housing with the aid of a screw. That method entails the danger that in actual usage in a motor vehicle during attendant changes in temperature and in the presence of vibrations the friction between the spring housing and the air-metering housing prove inadequate, thus letting the spring housing deviate from its intended pre-tensioned setting. Furthermore, in order to set the pre-tensioning of the spiral spring, the aforesaid screw must in each instance be first loosened, thereby removing the friction securing the spring housing, and then the screw must thereafter be retightened. As a result, the danger always exists that the threads of the screw connection will be damaged by continued use.